The present invention relates to a governor system and control method of a duplex steam turbine for a nuclear power plant and, a thermal power plant, or more particularly to a steam turbine governor system comprising a pair of governors for regulating the openings of turbine steam valves by a one-standby dynamic redundancy system, in which an abnormal one of the governors can be accurately discriminated by a simple device and function in the case where the difference between the output control signals of the governors exceeds a predetermined value.
A construction of the electro-hydraulic governor of the steam turbine with a pair of digital computers in duplex system is proposed in U.S. Pat. No. 4,153,198, wherein, even if one of the computers malfunctions, the turbine continues a normal operation by using the other computer, thereby assuring a high operating efficiency or high reliability. By virtue of these advantages, the system of the patent is broadly applied to various plants.
However, disadvantages of this system reside in the fact that it is difficult to determine which computer is to be used for regulating the turbine. Although each computer in the system is provided with a self-check system for detecting an abnormality or malfunction in hardware or software, if any, and change, upon detection of abnormality of one of the computers, the connection to the other computer for continued operation, it is still difficult in some cases to judge the abnormality or malfunction. For example, the two computers always execute the same process and produce respective outputs on the basis of the same inputs, and the turbine is driven by selected one of the outputs. Therefore, the two outputs must normally assume the same value. However, it is possible for the outputs to differ more than a tolerable range, while no abnormality is detected by the self-check function, although one of the computers must be abnormal or malfunctioning.
Under the above noted circumstances, it is necessary to provide an additional measure self check system for descriminating which of the outputs is correct. A well-known method of solution of this problem is to provide three computers which are used on the two-output-of-three basis, however, such a method results in high costs.